Blends of polycarbonate resins and polyester resins are known in the art. For example U.S. Pat. No. 3,128,372 discloses blends of polycarbonates and polyalkylene terephthalates; and U.S. Pat. No. 4,125,572 discloses blends of polycarbonates, poly(1,4-butylene terephthalate) and a copolyester of an aliphatic or cycloaliphatic diol and a mixture of terephthalic acid and isophthalic acid. Polycarbonate/polyester blends exhibit excellent properties which render them useful in the manufacture of film, fibers, and molded articles. They exhibit, for example, better ductility than neat polyesters and better processability than neat polycarbonates. There exist certain situations where polycarbonate/polyester blends exhibiting better impact properties than those possessed by conventional presently available polycarbonate/polyester blends are required.
It is known that the impact properties of neat polycarbonates can be upgraded by combining the polycarbonate resins with impact modifiers. U.S. Pat. No. 4,148,842 to Yu et al. discloses blends of a polycarbonate resin and an interpolymer modifier comprising crosslinked (meth)acrylate, cross-linked styrene-acrylonitrile, and uncrosslinked styrene-acrylonitrile. It is also known that the impact properties of neat polyester resins can be upgraded by combining said polyester resins with an impact modifier. U.S. Pat. No. 4,342,846 discloses blends of a polyester resin, such as polyethylene or polybutylene terephthalate, and an impact resistant interpolymer comprising cross-linked acrylic or methacrylic rubber, cross-linked styrene-acrylonitrile, and uncross-linked styrene-acrylonitrile. This type of impact modifier is described in U.S. Pat. No. 3,944,631 to Yu et al. as being a three stage interpolymer produced in a three stage polymerization process in which in the third stage a cross-linked acrylate/cross-linked styrene-acrylonitrile polymeric material is used as a reaction ingredient during the polymerization of styrene and acrylonitrile without a cross-linking agent.
It has now been discovered that a two phase material, i.e., a cross-linked acrylate/cross-linked styrene-acrylonitrile, produced by a two stage polymerization procedure, can be utilized as an effective impact modifier for blends of thermoplastic aromatic carbonate resins/polyester resins. The use of this two phase interpolymer comprised of a cross-linked elastomeric acrylate and a cross-linked styrene-acrylonitrile is thus a departure from known techniques described in the prior art. For example, in the aforediscussed U.S. Pat. Nos. 3,944,631, 4,148,842 and 4,342,846, three stage polymerizations yielding a three phase interpolymer comprised of a cross-linked acrylate/cross-linked styrene-acrylonitrile/uncross-linked or linear styrene-acrylonitrile, rather than a two stage polymerization yielding a two phase interpolymer followed by a blending step, are advocated.
The fact that the two phase cross-linked acrylate/cross-linked styrene-acrylonitrile interpolymer can be used effectively in a blend of aromatic carbonate resins and polyester resins as an impact modifier is generally surprising and unexpected. In order for a material to function as an effective impact modifier for thermoplastic resins it must not only improve the impact properties of these resins, but it must also be compatible with the resins. i.e., it must not deleteriously affect the advantageous properties of these resins. Furthermore, it must readily be combinable with the resin over the range of concentrations which are effective to improve the impact properties of these resins. While some materials are effective in positively upgrading the impact properties of certain resins they do so only at the cost of deleteriously affecting some of the other advantageous properties of said resins. While other materials function as impact modifiers for certain resins and do not significantly deleteriously affect substantially most of the advantageous properties of these resins they are not readily combinable with these resins. Still other materials need be present in relatively large concentrations in order to significantly positively upgrade the impact properties of these resins.
This area of impact modification of various resins by blending them with various compounds which function as impact modifiers is thus still an art rather than an exact science wherein the empirical approach is still generally the rule rather than an exception. This is particularly true when dealing with blends of two different resins, wherein the aforediscussed problems are greatly magnified.
Thus, the fact that the instant two phase interpolymers function as effective impact modifiers for blends of aromatic carbonate resins and polyester resins, are compatible with these blends, positively upgrade the impact properties of the blends at relatively low loadings, and are readily combinable with these blends, is one which could not be predicted and is unexpected.